This invention relates to intaglio and gravure printing cylinders and plates, and more particularly to low cost, plastic based, metal surface cylinders and plates and the manufacture thereof.
Generally, intaglio or rotogravure printing is obtained from cylinders mounted to rotate about their central axis with the outer peripheral surface of the cylinder having been etched with the particular information to be printed.
The prior art cylinders generally comprise an outer peripheral layer of copper which when ground and polished to the exact desired diameter is then etched in order to carry the particular information to be printed.
The prior art cylinders themselves generally comprise seamless tubing of steel or iron which has been cut to length and counterbored at its ends for the receipt of mounting gudgeons. The gudgeons are secured to the tubing in a variety of methods, such as welding, botling, etc. with shafts extending from the center of the gudgeons in order to mount the resulting cylindrical drum. The cylinder with the gudgeons and shaft is then mounted in a plating tank so that the entire outer peripheral surface of the cylinder is plated.
Once the plating process is completed, the copper surface is polished until the exact diameter required in the printing machine is obtained. Then, the image transfer ready cylinder is engraved or etched by one of a variety of well known methods, thereby embedding the desired information into the cylindrical surface. Finally, the cylinder is mounted in the rotogravure printing apparatus and printing is initiated.
The rotogravure printing process has long been known as a process having low waste, flexibility and unexcelled quality in the resulting print. However, in spite of these inherent qualities in the rotogravure and intaglio printing methods, this process has only been employed generally for long run production, because of the extremely high cost for the production of cylindrical bases.
One of the inherent features of the rotogravure printing process is its ability to print a complete 360 degrees while also being able to product an infinitely variable repeat of information, within the capabilities of the machinery, onto a roll of paper without any mismatch or registry problem, since the cylinder can be etched about its entire periphery if so required by the design. As a result, the rotogravure printing process is presently employed in the production of wallpaper, wrapping paper, printed boxes, package wrappers, as well as catalogues and magazines (as examples of publication and commercial printing applications), and other similar long run continuous patterned printed product lines where large rolls of paper or substrate can be continuously printed without interruption. Furthermore, it has only been economically feasible for such type of product lines to employ rotogravure printing since the high cost of tooling and setup can be amortized over the length of the run.
Aside from the difficulty and the expense of setting up present rotogravure cylinders, the prior art cylinders suffer from the inherent difficulty of having only firm contact with the rotation-inducing shaft at the ends of the cylinder where the gudgeons are mounted. Since the information to be printed is engraved or etched in the cylinder's surface, tonal variations of the ink density can be achieved by varying the depth of the etch as well as the area of the etch. As a result, considerable pressure is exerted by the impression roller against the etched surface of the printing cylinder in order to force the paper passing between them down into the etched depressions in the cylinder's surface, thereby receiving these tonal variations.
Due to this extreme pressure, the prior art cylinders have difficulty with the etched surface not coming into complete contact with the paper. This failure is generally due to internal bending of the cylinder against the pressure of the rollers or imperfect concentricity of the surface. As a result of the deflection and concentricity problems, any desired increasing of the effective length of a cylinder creates complex engineering problems. In some applications, solid steel drums have been employed to reduce the deflection problem, however such cylinders are obviously very expensive and extremely difficult to handle, as well as being very difficult to be made perfectly concentric to its central axis about the entire contact surface.
Another problem inherently found in prior art rotogravure cylinders is the difficulty of maintaining a high degree of balance throughout the cylinder as the cylinder rapidly rotates. The typical construction of prior art cylinders with end mounted gudgeons driving either a tubular structured cylinder or a solid, heavy metal mass, creates an intrinsically unbalanced cylinder. Since one major advantage of rotogravure printing is its high speed, any detectable cylinder unbalance, no matter how slight, will create an increasing problem, first with tonal variations and eventually with system breakdown.
Although prior art cylinders have been constructed with increasing tolerance levels being maintained, the basic structure of these prior art units prevents complete elimination of balance problems. In the first class of prior art cylinders, a solid heavy mass of metal is employed as the base. In this construction, balance can be minimized by extremely expensive machining procedures. However, since completely perfect balance is not economically feasible, the balance imperfections, however minor initially, become increasingly pronounced due to the unequal centrifugal pull exerted by this massive, heavy structure.
The other general class of prior art cylinders is tubular structured. These cylinders are inherently unbalanced, since insufficient internal rigidity is employed or gudgeon-like driving systems are used which are incapable of commercially feasible perfect balance.
The best known prior art are the references cited by the Examiner in my above-identified parent Application. However, these references are not believed to in any way teach or suggest the present invention. Although an extensive list of references were cited by the Examiner, the following are believed to be the most pertinent references:
______________________________________ Ballard U.S. Pat. No. 1,643,046 Koch French Patent 1,289,119 Hunn U.S. Pat. No. 2,872,349 Trzyna U.S. Pat. No. 3,693,544 Barker U.S. Pat. No. 3,832,948 ______________________________________
Ballard discloses the typical prior art rotogravure cylinders which employ solid metal cylindrical bases, or thick walled metal cylindrical shells, with the etchable metal affixed thereto.
In Koch, merely a plastic gravure plate and method of manufacturing thereof is disclosed. Koch shows in FIG. 4, a hollow, cylindrically-shaped multi-layered plastic construction, however, there is absolutely no teaching or suggestion as to the construction of the supportive base on which this hollow, cylindrical shell will be mounted and driven. Furthermore, the disclosure relating to FIG. 4 clearly shows that element 17 is an elongated electric lamp which extends along the axis of the hollow cylinder and is used to expose the gelatin layers forming the plate construction, in order to develop the layers in accordance with the disclosed process. There is no teaching or suggestion of any kind in Koch which in any way teaches a complete operative rotogravure printing cylinder or image-ready cylinder.
Similarly, both Trzyna and Hunn do not disclose an isotonic and isotropic plastic base construction which is capable of meeting the standards and criteria for an operative rotogravure printing cylinder. In Trzyna, the cylindrical core material was formed in place while Hunn discloses a carveable plastic cylinder for making a relief-type surface. Neither disclosure is capable of teaching a cylindrically-shaped molded plastic supportive base capable of performing as a base of a rotogravure printing cylinder.
In Barker, a flat plastic supporting base is taught which is directly etched in order to provide a printing master. This is completely divergent from the teaching of the present invention wherein plastic is employed as a supporting base only and is not directly etched. Furthermore, the plastic base of the present invention is surrounded with an etchable metal into which the printing information is etched.
None of the best known prior art references in any way teaches or suggests a lightweight molded plastic supportive base for an operative gravure or intaglio printing system, as defined in the present application, with its isotonic, isotropic, stress and void-free inherent characteristics as detailed in this present disclosure. These prior art references merely typify the problems, discussed in detail above, that have constantly faced the gravure printing field and have heretofore gone unresolved.
In the prior art gravure plates, the first generation or original plate is produced in a solid sheet of pure copper having a thickness ranging generally between 0.020 and 0.125 inches, and consequently, are heavy and expensive. Due to the high cost of investment required for a gravure plate to be etched or engraved, there is a complete lack in the industry of an image ready transfer gravure plate which could be maintained as a stock item ready for direct engraving and immediate use.